Many wind turbines utilize a gliding yaw bearing arrangement that allows the nacelle to rotate about the tower in a smooth and controlled manner. The yaw bearings absorb large static and dynamic loads and moments during the wind turbine operation, and provide for smooth rotational characteristics for the orientation of the nacelle under all weather conditions. Such wind turbines include the General Electric 1.x series of wind turbines that have been in use since approximately 2003.
Yaw bearing arrangements often use yaw pads that glide over a surface to provide a controlled degree of resistance to rotation. Yaw pad wear is a significant issue in all such wind turbine systems. When the yaw pads wear, the wind turbine performance suffers and often the wind turbine makes loud noises (sometimes referred to as “fog-horning”) which can be disruptive of the lives of people living near a wind turbine or wind farm. This also tends to cause yaw pad vibration which degrades the yaw pads by accelerating pad wear as well as sometimes causing splitting or other damage to the yaw pads.
Lubrication and proper pressure on the yaw pads can be used to reduce the possibility of fog-horning and extend the life of the yaw pads. Servicing the yaw pads to lubricate and properly torque the yaw piston assembly for correct pad pressure is time consuming and expensive. Each of the example GE wind turbines mentioned above typically includes 12 or 18 yaw pads (more or fewer may be used in any given wind turbine design) that should be periodically serviced. To service these yaw assemblies including yaw pad replacement, lubrication, reassembly and torqueing can be an entire day's work for a crew of two technicians. The work is carried out inside the nacelle of the wind turbine high in the air, and the wind turbine is shut down during such service. This not only results in high cost for the technician's time and equipment but also shuts down production of electricity which is a minimum of about 1.5 megawatts. Thus a ten hour maintenance shutdown can cost the operator the service labor costs plus parts cost plus opportunity costs equaling the value of up to 15 megawatt-hours or more of electricity production.
In addition, the work required to service the yaw assemblies can be quite challenging. The work is carried out high in the air inside a nacelle using tools and parts that have to be brought up with the technicians. Also, in many cases the yaw assemblies may be resting in tight spaces that may be difficult to access with the large tools currently required.